1. Field of the Invention
The present invention is a method for measuring the amount of inorganic metals and other contaminants that are extracted from a component upon exposure to liquids. In particular, the present invention is a method for dynamically measuring the extraction of contaminants from components of a chemical distribution system.
2. Description of the Related Art
Chemical distribution systems are commonly used to provide process chemicals from a central location to points of use in semiconductor fabrication facilities. Systems of this type are commercially available from a number of suppliers including FSI International of Chaska, Minn. Since the manufacturing yield and performance of semiconductor devices are sensitive to inorganic and other contaminants such as aluminum, calcium, iron and sodium, high-purity chemicals are used in the fabrication process.
Chemical distribution systems contain many components such as tanks, valves, filters and tubing that have the potential to add contaminants to the chemical being distributed. These contaminants are present both on the component surfaces exposed to the chemical, and in the bulk of the components. Following their assembly and installation at the semiconductor fabrication facility, and before being used in production, chemical distribution systems are therefore qualified to ensure that the concentrations of contaminants being added to the chemical by the system are below acceptable specification levels.
Qualification of chemical distribution systems requires the removal of the surface and bulk contaminants. Although the surface contaminants can be relatively easily removed by rinsing, the bulk contaminants must be removed by extraction. Conventional procedures for extracting contaminants are disclosed generally in the Grant et al. article, Issues Involved in Qualifying Chemical Delivery Systems for Metallic Extractables, published in FSI Technical Report TR 391 (June, 1993). In general, the extraction procedure disclosed in the Grant et al. article involves filling the system with chemical and allowing the chemical to remain in the system for a fixed period of time. Extraction is monitored by taking simultaneous samples of the chemical entering the system and at various locations throughout the system. The samples are then analyzed for contaminant concentrations. The change in concentration between the various sample points is assumed to be caused by extraction from the delivery system. If the change in concentration exceeds the specification, the chemical is drained from the system and the process repeated.
The decreasing feature size and continuing increase in the complexity of semiconductor devices makes the devices increasingly sensitive to contamination. Unfortunately, the conventional qualification procedures described above have a number of drawbacks. They are, for example, subject to a relatively large potential for error. Sources of error include sample collection and handling, and variations in the background contaminant levels of the incoming chemical. The procedures are also relatively inefficient since continuing supplies of incoming chemical are required. They also provide information on the extraction characteristics of the systems only over the extraction period that the samples are taken.
There is, therefore, a continuing need for improved chemical extraction and qualification procedures. In particular, there is a need for faster and more accurate and efficient extraction and qualification procedures. Procedures of this type that can also be used to accurately predict the future extraction characteristics of the system would be especially desirable.